The present disclosure relates generally to electrical interconnections for connecting printed circuit boards (“PCBs”).
Electrical connectors are used in many electronic systems. It is generally easier and more cost effective to manufacture a system on several PCBs that are connected to one another by electrical connectors than to manufacture a system as a single assembly. A traditional arrangement for interconnecting several PCBs is to have one PCB serve as a backplane. Other PCBs, which are called daughter boards or daughter cards, are then connected through the backplane by electrical connectors.
Connectors in different formats are used, depending on the types or orientations of PCBs to be connected. Some connectors are right angle connectors, meaning that they are used to join two printed circuit boards that are mounted in an electronic system at a right angle to one another. Another type of connector is called a mezzanine connector. Such a connector is used to connect printed circuit boards that are parallel to one another.
Examples of mezzanine connectors may be found in: U.S. patent application Ser. No. 12/612,510, published as U.S. Patent Application Publication No. 2011-0104948; International Application No. PCT/US2009/005275, published as International Publication No. WO/2010/039188; U.S. Pat. No. 6,152,747; and U.S. Pat. No. 6,641,410. All of these patents and patent applications are assigned to the assignee of the present application and are hereby incorporated by reference in their entireties.
Electronic systems have generally become smaller, faster and functionally more complex. These changes mean that the number of circuits in a given area of an electronic system, along with the frequencies at which the circuits operate, have increased significantly in recent years. Current systems pass more data between printed circuit boards and require electrical connectors that are electrically capable of handling more data at higher speeds than connectors of even a few years ago.
One of the difficulties in making a high density, high speed connector is that electrical conductors in the connector can be so close that there can be electrical interference between adjacent signal conductors. To reduce interference, and to otherwise provide desirable electrical properties, metal members are often placed between or around adjacent signal conductors. The metal acts as a shield to prevent signals carried on one conductor from creating “crosstalk” on another conductor. The metal also impacts the impedance of each conductor, which can further contribute to desirable electrical properties.
As signal frequencies increase, there is a greater possibility of electrical noise being generated in the connector in forms such as reflections, crosstalk and electromagnetic radiation. Therefore, the electrical connectors are designed to limit crosstalk between different signal paths and to control the characteristic impedance of each signal path. Shield members are often placed adjacent the signal conductors for this purpose.
Crosstalk between different signal paths through a connector can be limited by arranging the various signal paths so that they are spaced further from each other and nearer to a shield, such as a grounded plate. Thus, the different signal paths tend to electromagnetically couple more to the shield and less with each other. For a given level of crosstalk, the signal paths can be placed closer together when sufficient electromagnetic coupling to the ground conductors is maintained.
Although shields for isolating conductors from one another are typically made from metal components, U.S. Pat. No. 6,709,294, which is assigned to the same assignee as the present application and is hereby incorporated by reference in its entirety, describes making an extension of a shield plate in a connector from conductive plastic.
In some connectors, shielding is provided by conductive members shaped and positioned specifically to provide shielding. These conductive members are designed to be connected to a reference potential, or ground, when mounted on a printed circuit board. Such connectors are said to have a dedicated ground system.
In other connectors, all conductive members may be generally of the same shape and positioned in a regular array. If shielding is desired within the connector, additional conductive members may be connected to an AC-ground. All other conductive members may be used to carry signals. Such a connector, called an “open pin field connector,” provides flexibility in that the number and specific conductive members that are grounded, and conversely the number and specific conductive members available to carry signals or power, can be selected when a system using the connector is designed. However, the shape and positioning of conductive members providing shielding is constrained by the need to ensure that those conductive members, if connected to carry a signal rather than providing a ground, provide a suitable path for signals.
Other techniques may be used to control the performance of a connector. For example, transmitting signals differentially can also reduce crosstalk. Differential signals are carried by a pair of conducting paths, called a “differential pair.” The voltage difference between the conductive paths represents the signal. In general, a differential pair is designed with preferential coupling between the conducting paths of the pair. For example, the two conducting paths of a differential pair may be arranged to run closer to each other than to adjacent signal paths in the connector. Conventionally, no shielding is desired between the conducting paths of the pair, but shielding may be used between differential pairs.
Examples of differential electrical connectors are shown in U.S. Pat. No. 6,293,827, U.S. Pat. No. 6,503,103, U.S. Pat. No. 6,776,659, and U.S. Pat. No. 7,163,421, all of which are assigned to the assignee of the present application and are hereby incorporated by reference in their entireties.
Differential connectors are generally regarded as “edge coupled” or “broadside coupled.” In both types of connectors the conductive members that carry signals are generally rectangular in cross section. Two opposing sides of the rectangle are wider than the other sides, forming the broad sides of the conductive member. When pairs of conductive members are positioned with broad sides of the members of the pair closer to each other than to adjacent conductive members, the connector is regarded as being broadside coupled. Conversely, if pairs of conductive members are positioned with the narrower edges joining the broad sides closer to each other than to adjacent conductive members, the connector is regarded as being edge coupled.
Electrical characteristics of a connector may be controlled through the use of absorptive material. U.S. Pat. No. 6,786,771, which is assigned to the same assignee as the present application and which is hereby incorporated by reference in its entirety, describes the use of absorptive material to reduce unwanted resonances and improve connector performance, particularly at high speeds (for example, signal frequencies of 1 GHz or greater, particularly above 3 GHz). U.S. Pat. No. 7,371,117, U.S. Pat. No. 7,581,990, and U.S. patent application Ser. No. 13/029,052, published as U.S. Patent Application Publication No. 2011-0230095, which are assigned to the assignee of the present application and are hereby incorporated by reference in their entireties, describe the use of lossy material to improve connector performance.